1. Field of the Invention
The invention relates to photographic apparatus in general and, more particularly, to a novel latching mechanism for releasably securing a film loading door of such apparatus.
2. Description of the Prior Art
Photographic apparatus using film cassettes within which is stacked a plurality of film units are well known. The film unit on top of the stack is urged into a position abutting an exposure opening in the cassette, by a spring acting between the film unit at the bottom of the stack and underlaying cassette structure. Initially, the exposure opening is closed by a so-called dark slide to prevent unintended exposure of the film before the cassette is secured within a receiving chamber of the apparatus. As an added element, the cassette houses a substantially flat electrical battery which serves to provide power to a plurality of electrical components of the photographic apparatus.
Photographic apparatus suited for sequentially exposing the film units within a cassette of the kind referred to may be similar to the apparatus described in U.S. Pat. Nos. 3,750,551, 3,760,701, and 3,774,516. Hence, the apparatus may be provided with a door movable between open and closed positions to render an exposure chamber within the apparatus accessible for insertion or removal of a film cassette. The door may be releasably retained by a latch mechanism and may be cooperating with an electrical switch for energizing an electrical control circuit of the apparatus by the battery located within the cassette, when the door is in its closed position. A connection between the battery and the control circuit is established by electrical contact members positioned in the exposure chamber at a location where they may engage electrodes of the battery through apertures appropriately positioned in the film cassette.
The film within the cassette is protected from unintended exposure to light by a dark slide covering the top film unit of the stack. Once the cassette has been inserted into the exposure chamber, the door has been secured and the cooperating switch has established an electrical connection between the battery and the control circuit, the latter may be activated automatically to remove the dark slide from the cassette and to eject it out of the photographic apparatus.
The operation of the apparatus has been described in U.S. Pat. No. 3,774,516 as comprising a pre-exposure phase, an exposure phase, and a post-exposure phase executed seriatim in an automatic manner. The pre-exposure phase may include an automatic focusing operation, for instance as described in U.S. Pat. No. 4,200,378. After the lens has been properly focused, the apparatus executes an exposure phase which in the example of U.S. Pat. No. 3,774,516 consists of shutter closure, movement of a reflex member from a viewing position to an exposure position, shutter opening and closing to expose the film possibly accompanied by the firing of a flash, subsequent return of the reflex member to its viewing position in which, incidentally, it seals the film in the cassette from light, and opening of the shutter. The post-exposure phase causes removal of the exposed film unit from the cassette to the outside of the camera, through power-driven rollers. Movement of the film unit through the rollers may entail processing of the film unit by rupture of a pod of processing composition integral with the film unit and the spreading of the composition over the entire light-sensitive surface of the film unit as a coating of uniform thickness, to initiate a diffusion transfer process in a manner well known in the art.
Removal of the dark slide from the cassette to the outside of the apparatus is accomplished by bypassing the pre-exposure and exposure phases of the operation of the apparatus and by resorting, instead, to what essentially amounts to the post-exposure phase only, i.e., the dark slide is ejected in the same manner as an exposed film unit.
This is made possible by a control switch which reacts to removal of a film cassette from the apparatus by assuming a condition by which the control circuit suppresses the pre-exposure phase and the exposure phase of operation. The control switch advantageously cooperates with a film indexing or counting device which is reset in response to insertion of a cassette into the apparatus. Insertion into the apparatus of a fresh film cassette and actuation of the switch energizing the control circuit by closure of the film loading door thus causes ejection of the dark slide followed by resetting the control switch to a state in which pre-exposure and exposure phases are again made part of the operational cycle of the apparatus at least as long as there are film units in the cassette as determined, for instance, by the film indexing mechanism or counter provided in the apparatus. While ejection of the dark slide occurs automatically in response to closure of the film loading door, pre-exposure and exposure operational phases require operator assistance. For a more detailed discussion of this operation, reference may be had to U.S. Pat. No. 3,750,551.
The door latch of the prior art has been found to function satisfactorily in most instances. However, it comprises comparatively many parts, and relatively complicated linkages for actuation of the switch responsive to movement of the door.